Many multiphase fluidic applications require mixing or at least enhancement of interfacial area. In micro-fluidic systems, typical dimensions are below 1 mm and make the mixing and/or the agitation a first order issue. Indeed the typical flows often involved in these applications are creeping flows in which two initial miscible or non miscible fluids hardly mix by themselves (turbulence in fluid flows being commonly used for achieving mixing in large-scale fluid systems). Increasing the interfacial area between two fluids or mixing at very small scales without external stirring or mechanical action is very difficult because of the low Reynolds numbers involved, especially for nearly two dimensional geometries. Therefore, reaction processes are largely diffusion limited.
The concept of mixing liquids in a path is necessary to create adequate liquid flow in a micro reactor system or more particularly, in a mixer design or module within a micro reactor system. Typically, there is a source of reactants or a least a plurality of fluid connections for delivering reactants at an injection zone for upstream flow. Typically, liquids in the prior art include water, aqueous and organic liquid solutions.
Many have developed mixers of several types to generate mixing in micro systems. Whatever mixing solution is chosen, the mixer may be implemented within a complete micro system. The required attributes for the mixers are therefore extended beyond mixing efficiency, whereby mixer dimensions can preferably be changed to affect pressure drop, but not affect mixing efficiency or at least have a minimum effect on mixing efficiency.
In such micro reactor systems, it is therefore desirable to have a mixer with maximum efficiency at very low pressure drop. Furthermore, it is desirable to generate appropriate mixing within the structure of the path.
Prior art approaches for performing the above described desired capabilities that are known in the art include the following examples.
For instance, a typical split and recombine solution is shown in FIG. 1 and described in U.S. Pat. No. 5,904,424 A1 entitled “Device for Mixing Small Quantities of Liquids”. In this patent, in order to reduce the length over which the reactants need to diffuse, the inlet reactant streams are separated and recombined in a multi-layered structure.
Further prior art implementations of this principle are disclosed by IMM. (Refer to http://imm.mediadialog24.de/v0/vvseitene/vvleistung/misch2.html). Here, the IMM mixing split-recombine concept of caterpillar mixers includes two unmixed fluid streams divided such that two new regions are formed and are further down recombined. All four regions are ordered alternatively next to each other such that the original geometry is re-established.
There are also prior art three-dimensional flows that represent chaotropic solutions. These designs solve the problem of mixing by creating a transverse flow without requiring the use of moving mixer elements. Another similar prior art chaotropic mixer can be found for instance, in International Publication Number WO03/011443A2, entitled, “Laminar Mixing Apparatus and Methods” assigned to the President and Fellows of Harvard College. Here, the helical flow is created by weak modulations of the shape of the walls of the channel, or by grooves defined on the channel wall allowing mixing of a fluid with a Reynolds number of less than 100 thereby capably mixing a fluid flowing in the micro-regime. A similar prior art structure is shown in FIG. 2.
Cellular Process Chemistry (CPC), a German company, cites a design using liquid slugs and a decompression chamber in European Patent Application EP1123734A2 entitled “Miniaturized Reaction Apparatus” published on Aug. 16, 2001 as shown in FIG. 3.
Disadvantages of these prior art solutions will be outlined below. For instance, with respect to the first prior art approach, split and recombine design requires significant dimensional precision for the manufacture of these designs. This is necessary to ensure that the upstream flow splits equally in each sub-channel before the recombination, so that the flowrates ratio of the liquid that are mixed is equal to the inlet ratio set by the user.
The second approach utilizing three-dimensional or chaotropic flows has several drawbacks, one being the aspect ratio between the height and width of the channel, another being costly technology, and yet another being that it is useful for liquids only and not gas-liquid systems.
The third prior art approach, the liquid slugs device similarly has all the drawbacks of those approaches described above. Its only advantage is that low pressure drop due to parallelization and decompression reduces dimensions efficiently.
All the above devices have great difficulty achieving low pressure drop. This is generally thought to be caused by the prior art designs' attempts at reducing dimensions to enhance mixing efficiency thereby dramatically increasing the pressure drop, which is a penalty.
A new approach is needed that preferably overcomes the disadvantages of any of the prior art solutions above that provide optimal pressure drop by tuning inner dimensions; localized liquid flow at geometric obstacles and restrictions in the path structure; mixing generated in the path structure via obstacles and by reducing local dimensions; fully three dimensional flow between obstacles; control at the initial contact region at injection; and robustness of efficiency with respect to fluids.
The term fluid is herein defined as including miscible and immiscible liquid-liquids, gas-liquids and solids.